222 TANNINS 



amount of tannin, more especially in germinating seeds, van 

 Wisselingh points out that the amount found at any particular 

 moment represents the balance as it were of the tannin ac- 

 count ; that is to say, if more tannin is formed than is decom- 

 posed, an increase in the tannin content will result and vice 

 versa, so that in one and the same plant there will be some- 

 times an increase and sometimes a decrease according to the 

 conditions obtaining. It does not necessarily follow, and this 

 is applicable to many things besides tannin, that because there 

 is an increase in the amount, therefore the substance is of no 

 value in constructive metabolism. 



Tannin has been considered an important constituent of 

 the osmotic substances of the cell ; although this may be true 

 for some tannins it probably does not hold for all, since no 

 ill effects follow the precipitation of tannins in the living cell 

 by means of methylene blue ; also, in certain cases, it is not 

 renewed when precipitated. 



A biological significance is not infrequently attached to 

 tannins; thus it may be of use against animals, it may be 

 connected with the activity of nectaries in providing sugar, 

 and it has been suggested by Moore that when it occurs in 

 the epidermis of leaves, it may play a part in the opening and 

 closing of stomata. 



Finally, it may be of considerable value as an antiseptic, 

 preventing the germination and growth of parasitic Fungi. In 

 this connexion Cook and Taubenhaus * have found that in 

 many cases tannin has a tendency to retard or inhibit the 

 growth of Fungi, the parasitic forms being more sensitive than 

 the saprophytic. In some cases the spores are killed, whilst 

 in others germination is much impeded. On the other hand, 

 low percentages of tannin may in some instances stimulate 

 germination and also fruiting. The behaviour of Fungi 

 towards tannin varies with the species and sometimes even 

 with the individual, more especially in the case of spores. 



To conclude, the different substances included under the 

 term Tannin are so numerous as to make it improbable that 

 they all have the same physiological significance. 



*Cook and Taubenhaus: "Delaware Coll. Agric. Exper. Station" Bull., 



91, 1911. 



